Handle 'infinite' and 'unknown' capacity in CapacityWeigher
Handle 'infinite' and 'unknown' capacity in CapacityWeigher

This patch updates CapacityWeigher to transform 'infinite' and
'unknown' capacity reported by back-ends to float('inf').  They
are considered the same for sorting purpose.

Change-Id: Ic8f811227c9937c4e09eb8b77457ed7e9231be4e

Accelerite/cinder,apporc/cinder,cloudbase/cinder,maelnor/cinder,blueboxgroup/cinder,alex8866/cinder,petrutlucian94/cinder,bswartz/cinder,spring-week-topos/cinder-week,potsmaster/cinder,julianwang/cinder,rickerc/cinder_audit,github-borat/cinder,Hybrid-Cloud/cinder,hguemar/cinder,nexusriot/cinder,nikesh-mahalka/cinder,sasukeh/cinder,NetApp/cinder,duhzecca/cinder,tlakshman26/cinder-new-branch,saeki-masaki/cinder,sasukeh/cinder,maelnor/cinder,cloudbau/cinder,JioCloud/cinder,phenoxim/cinder,takeshineshiro/cinder,spring-week-topos/cinder-week,eharney/cinder,Accelerite/cinder,abusse/cinder,abusse/cinder,dims/cinder,eharney/cinder,j-griffith/cinder,dims/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,tlakshman26/cinder-new-branch,rakeshmi/cinder,redhat-openstack/cinder,winndows/cinder,nikesh-mahalka/cinder,Thingee/cinder,leilihh/cinder,openstack/cinder,cloudbase/cinder,petrutlucian94/cinder,Paul-Ezell/cinder-1,NeCTAR-RC/cinder,ntt-sic/cinder,Thingee/cinder,Datera/cinder,duhzecca/cinder,inkerra/cinder,inkerra/cinder,ntt-sic/cinder,github-borat/cinder,rakeshmi/cinder,Paul-Ezell/cinder-1,JioCloud/cinder,alex8866/cinder,ge0rgi/cinder,hguemar/cinder,julianwang/cinder,blueboxgroup/cinder,tlakshman26/cinder-https-changes,tlakshman26/cinder-https-changes,Hybrid-Cloud/cinder,CloudServer/cinder,nexusriot/cinder,manojhirway/ExistingImagesOnNFS,scottdangelo/RemoveVolumeMangerLocks,potsmaster/cinder,Akrog/cinder,Nexenta/cinder,Nexenta/cinder,NeCTAR-RC/cinder,scality/cinder,redhat-openstack/cinder,mahak/cinder,rickerc/cinder_audit,Thingee/cinder,apporc/cinder,Akrog/cinder,scality/cinder,NetApp/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,CloudServer/cinder,j-griffith/cinder,leilihh/cinder,phenoxim/cinder,mahak/cinder,winndows/cinder,takeshineshiro/cinder,scottdangelo/RemoveVolumeMangerLocks,saeki-masaki/cinder,openstack/cinder,Datera/cinder,bswartz/cinder,manojhirway/ExistingImagesOnNFS,cloudbau/cinder